The present invention relates to self-drilling fasteners having a drill portion which is detachable or frangible from a threaded portion, a method of fastening using a self-drilling fastener of the present invention, and a drive tool for use with a self-drilling fastener of the present invention.
Numerous fasteners are available which provide self-drilling features. In many applications, self-drilling fasteners, such as drill screws, are advantageous as the holes and threads are drilled and formed by the fastener in a single driving application. Self-drilling fasteners eliminate the additional assembly steps of drilling and tapping holes before driving of the fastener. As such, self-drilling fasteners may be highly advantageous by reducing preparation and assembly time, cost and effort.
Self-drilling fasteners are designed with a shank having a head formed at one end, a drill-tip portion at the end opposite the head, and a threaded portion intermediate the drill portion and head. The drill-tip portion is provided with a chisel point and cutting edge which drill into the workpiece material forming a hole for engagement by the threaded portion. The drill portion is sized and dimensioned to provide a hole having a predetermined diameter which provide positive engagement of the thread portion, for cold forming or swaging internal threads thereon.
While self-drilling fasteners of the type briefly described hereinabove have provided many advantages, use of such fasteners in some situations may not provide desirable finished results. For example, in applications where the thickness dimension of the workpiece is less than the total length of the shank of the fastener, the drill-point may protrude from the workpiece. This may be undesirable as it may result in a point extending from a surface or may merely appear to be unfinished or otherwise aesthetically undesirable. Additionally, the drill-point is not required in the workpiece since often it does not include threads and therefore does not provide substantial mechanical advantage or any clamping function in joining the workpieces, as compared to the threaded portion.